This invention relates to analysis of materials, and more particularly, relates to method and apparatus for the decomposition and quantitative determination of the amount of nitrogen in a sample.
A common form of sample preparation for elemental analysis involves the combustion of a sample followed by the use of the combustion gases from this sample for the detection of the desired constituent(s) or analyte(s). Examples of this include halogen and sulfur determination using a microcouloumetry, nitrogen determination by chemiluminescence of excited state nitrogen dioxide, sulfur determination using SO.sub.2 fluorescence, and carbon and hydrogen determination by gravimetric or Pregl-Dumas techniques. With the exception of carbon and hydrogen determinations, there is a problem associated with the combustion process which can cause unreliable analytical results and this problem centers on the sample introduction step.
If the sample is introduced using a syringe needle the needle must be placed directly into or very close to the hot zone of a combustion furnace to ensure the sample is transferred into the combustion zone and combusted therein. Unfortunately, heavy organic fractions or salts can remain within the needle and possibly clog it temporarily, or permanently, as well as the hostile environment damaging the needle. One approach taken to overcome this problem is to introduce the sample into the hot portion of the furnace using a small boat which has been loaded with the sample when the boat was positioned in a relatively cool portion of the furnace tube. In either case, however, the sample introduction and subsequent combustion is a transient process. Therefore, the oxygen concentration in the combination tube changes over time during this process. This can be detrimental in cases where equilibria involving oxygen are important to the instrumental stability, sensitivity, or detection limits.
Accordingly, there is a need for a sample introduction scheme to allow for longer integration times in the detection phase which would then improve detection limits and also allow for use as an on-line monitor in process control, or as a chromatographic detector.
These and other limitations and disadvantages of the prior art are overcome by the present invention, however, and an improved method and apparatus are provided for analysis of samples for nitrogen.